1. Field of the Invention
The invention relates to an all-solid battery and a method for manufacturing the all-solid battery.
2. Description of Related Art
A lithium ion secondary battery has an energy density higher than that of a conventional secondary battery and can be operated at high voltages. Therefore, it is used in information instruments such as a cellular phone and the like as a secondary battery that can be readily down-sized and light-weighted. In recent years, the lithium ion secondary battery also has a high demand for large engines such as those in electric vehicles, hybrid vehicles, and the like.
A lithium ion secondary battery has a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed therebetween. As the electrolyte used in the electrolyte layer, for example, a nonaqueous liquid or solid substance is known. When the liquid electrolyte (hereinafter, referred to as “electrolytic solution”) is used, the electrolytic solution is likely to permeate to the inside of the positive electrode layer or negative electrode layer. Therefore, an interface is likely to be formed between an active material contained in the positive electrode layer or negative electrode layer and the electrolytic solution, and performance is likely to be improved. However, since the broadly used electrolytic solution is inflammable, a system for securing safety has to be mounted. On the other hand, when a solid electrolyte that is non-flammable (hereinafter, referred to as “solid electrolyte”) is used, the system can be simplified. Therefore, a lithium ion secondary battery (hereinafter, referred to as “all-solid battery”) having a form provided with a layer that contains the solid electrolyte (hereinafter, referred to as “solid electrolyte layer”) is under development.
As a technique relating to such an all-solid battery, Japanese Patent Application Publication No. 2011-060649 (JP 2011-060649 A), for example, discloses an electrode active material layer that includes an electrode active material, and a sulfide solid electrolyte material that fuses to a surface of the electrode active material and does not substantially contain cross-linked sulfur, and an all-solid battery provided with the electrode active material layer. Further, Japanese Patent Application Publication No. 2012-094437 (JP 2012-094437 A) discloses an all-solid battery that includes a positive electrode active material layer that contains a positive electrode active material, a negative electrode active material layer that contains a negative electrode active material, and a solid electrolyte layer formed between the positive electrode active material layer and negative electrode active material layer. In the all-solid battery, the solid electrolyte layer is obtained by powder compacting the solid electrolyte material, and in a gap between the solid electrolyte materials an insulating material having a withstand voltage higher than argon is disposed.
In the all-solid battery, from a viewpoint that performance can be readily improved, a sulfide solid electrolyte is used as the solid electrolyte in some cases. Also in Japanese Patent Application Publication Nos. 2011-060649 and 2012-094437 (JP 2011-060649 A and JP 2012-094437 A), an all-solid battery that includes a negative electrode layer containing a sulfide solid electrolyte is described. Further, Cu is broadly used as a negative electrode current collector for all-solid batteries because it has low electric resistivity, can be readily processed, and is low in cost. Also in JP 2011-060649 A and JP 2012-094437A, it is described that Cu is used as the negative electrode current collector.
However, in the all-solid battery that includes a negative electrode that contains sulfur (a negative electrode layer that contains a sulfide solid electrolyte, for example), when a metal that reacts with sulfur such as Cu is used in the negative electrode layer, a problem that the metal reacts with sulfur and electronic conduction resistance tends to increase in an interface between the negative electrode layer and the negative electrode current collector is apprehended (see Japanese Patent Application Publication No. 2012-49023 (JP 2012-49023 A).